Interpretive Summary: A plant-induced cleft palate goat model was used to evaluate and compare age based surgical methods of cleft palate repair. Cleft palate repair surgery at a young age (2 months) in the goat model was effective at decreasing the percentage of injury-susceptible type 2 fibers to injury-resistant type 1 fibers when compared to surgery in older goats. Because fiber-type transformations appear to be necessary for changes in injury susceptibility, perhaps the success of repair is dependent on age. The implication then would be to repair palates in children earlier to promote fiber-type conversions to type 1 fibers. Further investigation of the factors that predispose muscle fibers to convert to type 1 fibers following surgery may help to decrease the percentage of type 2 fibers that remain and improve palatal movement and decrease the incidence of post surgical velopharyngeal incompetence.

Technical Abstract:
Despite cleft palate repair, velopharyngeal competence is not achieved in ~ 15% of patients, often necessitating secondary surgical correction. Velopharyngeal competence postrepair may require the conversion of levator veli palatini muscle fibers from injury-susceptible type 2 fibers to injury-resistant type 1 fibers. As an initial step to determining the validity of this theory, we tested the hypothesis that, in most cases, repair induces the transformation to type 1 fibers, thus diminishing susceptibility to injury. Single permeabilized levator veli palatini muscle fibers were obtained from normal palates and nonrepaired congenitally-clefted palates of young (2months old) and adult (14 to 15 months old) goats and from repaired palates of adult goats (8 months old). Repair was done at 2 months of age using a modified von Langenbeck technique. Fiber type was determined by contractile properties and susceptibility to injury was assessed by force deficit, the decrease in maximum force following a lengthening contraction protocol expressed as a percentage of initial force. For normal palates and cleft palates of young goats, the majority of the fibers were type 2 with force deficits of ~ 40%. Following repair, 80% of the fibers were type 1 with force deficits of 20% plus or minus 2%; these deficits were 45% of those for nonrepaired cleft palates of adult goats (p > .0001). The decrease in the percentage of type 2 fibers and susceptibility to injury may be important for the development of a functional levator veli palatini muscle postrepair.